Add basic lexenv support

src/stack.c

@@ -161,7 +161,7 @@ static inline void add_local_refs_for_object_sub_vals(LispVal *seen_objs,
         break;
     }
     case TYPE_STRING:
-        // ho held refs
+        // no held refs
         break;
     case TYPE_FIXNUM:
     case TYPE_FLOAT:
@@ -190,3 +190,31 @@ void compact_stack_frame(struct StackFrame *restrict frame) {
     lisp_realloc(refs->blocks, sizeof(struct LocalReferencesBlock *));
     refs->num_blocks = 1;
 }
+
+bool set_lexical_variable(LispVal *name, LispVal *value,
+                          bool create_if_absent) {
+    assert(the_stack.depth != 0);
+    DOTAILS(rest, LISP_STACK_TOP()->lexenv) {
+        if (EQ(XCAR(rest), name)) {
+            RPLACA(XCDR(rest), value);
+            return true;
+        }
+    }
+    if (create_if_absent) {
+        new_lexical_variable(name, value);
+    }
+    return create_if_absent;
+}
+
+void new_lexical_variable(LispVal *name, LispVal *value) {
+    assert(the_stack.depth != 0);
+    LISP_STACK_TOP()->lexenv =
+        CONS(name, CONS(value, LISP_STACK_TOP()->lexenv));
+}
+
+void copy_parent_lexenv(void) {
+    assert(the_stack.depth != 0);
+    if (the_stack.depth > 1) {
+        LISP_STACK_TOP()->lexenv = the_stack.frames[the_stack.depth - 2].lexenv;
+    }
+}